The present invention relates to a method for dewaxing oil, in particular to a dewaxing method in which the oil is pre-dried and after the formation of solid wax by cooling, the solid wax is removed by microfiltration.
Oils, extracted from vegetable and animal tissues, contain a number of impurities, which have to be removed in order to make the oil suitable for human consumption. One type of impurities consists of waxes, which are high melting esters of fatty alcohols and fatty acids, having a low solubility in oils. These waxes make the oil cloudy at lower temperatures. The quantity of waxes in crude oils varies from several hundred ppm to several thousand ppm. The wax content has to be reduced to a level of about 10 ppm or less, so that the cold stability of the oil is improved.
A method for dewaxing oil consists of carefully cooling the oil, followed by crystallization of the wax, which is then removed by centrifugation or filtration.
G. Haraldsson describes in a publication entitled "Degumming, dewaxing and refining" in JAOCS, vol. 60, page 203A-208A, several dewaxing processes, in which oil to be dewaxed is mixed with 4-6% by wt water, so that a soapy water phase is formed, which is easily removable by centrifugation.
K.-H. Brunner discloses in a Westfalia brochure entitled "New process developments in the field of edible oil refining with centrifugal separators" a dewaxing process which takes place after caustic refining. The oil is mixed with a certain amount of water, so that an optimal separation of the phases after crystallization is obtained. Crystallization takes place at about 5.degree. C. and a holding time of 6-8 hours. The crystallized wax is removed by centrifugation.
G. Rivarola et al discloses in an article entitled "Crystallization of waxes during sunflowerseed oil refining" in JAOCS, vol 62, page 1508-1513, specific dewaxing conditions so that the separation of the crystallized wax is improved. These optimal crystallization conditions comprise low cooling rates and low temperature differences between the oil and the coolant medium. It is recommended to add water to the oil to be dewaxed in order to improve wax separation in the aqueous phase.
Finally, DE-C-3,312,573 discloses a dewaxing method, in which after wax crystallization the wax crystals are removed by microfiltration using a microfilter having pore diameters of 0.05 to 5 .mu.m. The oil to be refined has a water content of 2.4% by wt.